Gas turbine engines, as well as other turbine systems such as turbochargers, compressors, fan assemblies, generators, auxiliary power units, and the like, typically include a gas compression section feeding a combustion chamber that produces hot gases to drive the turbine stages downstream. The engine compression section typically includes a plurality of moving bladed disks, separated by successive stages of stator vanes that redirect the gas flow.
While some conventional stator vanes are fixed in orientation (that is, they are only capable of redirecting airflow in one direction), other stator vanes known in the prior art are configured as “variable-pitch” vanes: that is, the angular position of a variable-pitch vane about its pivotable radial axis can be selectively adjusted in order to improve compressor performance at different engines speeds and operating conditions. The variable-pitch vanes are oriented using a mechanism known as a variable-pitch actuation and drive mechanism. There are various designs of such mechanisms, but on the whole, they all include one or more actuators fixed to the engine casing, synchronization bars or a control shaft, rings surrounding the engine and positioned transversely with respect to the axis thereof, and substantially axial levers also known as pitch control rods, connecting the rings to each of the variable-pitch vanes. The actuators rotate the rings about the engine axis and these cause all the levers to turn synchronously or asynchronously about the vane pivots. Other variable-pitch mechanisms will be known to those having ordinary skill in the art, particularly as implemented on auxiliary power units (APU).
Additionally present within the engine compression section are one or more structural frame elements that extend radially from the compression section hub to the engine casing to provide structural support in the compression section. For example, a typical compression section frame includes the annular outer structural casing disposed coaxially with the annular inner structural casing, or hub, with a plurality of circumferentially spaced apart struts extending radially therebetween and suitably fixedly joined thereto. The struts are suitably sized to provide a rigid frame for carrying the bearing loads from the hub radially outwardly to the casing.
While these structural frame elements are easily incorporated with fixed-pitch stator vanes, turbine engine compression section configurations with variable-pitch vanes include the radially-extending structural frame elements positioned upstream (with regard to the flow of gas) from the variable-pitch vanes. This configuration adds length and weight to the engine, but is required because of the space necessary to implement the synchronization bars, control shaft, rings, axial levers, and pitch control rods of the variable-pitch mechanism. That is, the space claim and complexity of the variable-pitch mechanism has heretofore effectively excluded the integration of the structural frame elements within (or in the same area as) the variable-pitch mechanism. Additionally, when the vanes are rotated, they require additional space circumferentially both due to the swinging of the vane edges and also the buttons (platforms) that these vanes need to be placed upon (at least at the outer diameter where they are driven). This means they have to be place relatively far away from the struts circumferentially. Since the struts do not move, the airflow out of this “combined” system would be very non-uniform—turning where the variable pitch vanes are and not turning where the struts are. This causes detrimental aerodynamic and mechanical responses from the downstream rotor.
More recent approaches to compression section flow control attempt to achieve the same flow vectoring as the conventional variable-pitch mechanism, but without the need for moving (i.e., rotating, translating) parts, and thus without the need for as much space claim. These more recent approaches typically fall into one of two classes: fluidic flow control approaches and plasma flow control approaches. First, with regard to fluidic flow control approaches, air is injected and/or removed from the flow stream that one desires to influence. Often, the goal is to avoid or eliminate boundary layer “separation,” which is a condition where the low velocity fluid near a solid boundary (wall) reverses in direction relative to the bulk of the flow. High velocity air may be injected to “energize” that boundary layer or the boundary layer may be sucked out. In some cases, a slot or series of holes will be used to pulse air in and out locally. Some common fluidic control devices include: steady blowing (continuous, constant injection); unsteady blowing (injection that various at an advantageous frequency); steady and unsteady suction; Coanda jets; and synthetic jets.
Second, with regard to plasma flow control approaches, an electric potential is provided to a device that causes air near the device to ionize. Because of the potential, the device also induces an electric field. The electric field exerts a force on the ionized particles that imparts momentum in a desired direction. As with fluidic control devices, plasma control devices tend to be placed on a solid boundary (wall) in order to influence the boundary layer in a beneficial way. Some common plasma flow control devices include: single dielectric barrier discharge (SDBD); micro- and nano-pulsing plasma actuators; and sliding discharge plasma actuators.
As with the variable-pitch configurations described above, the fluidic control and plasma control configurations known in the prior art have all employed structural frame elements that are located upstream of the flow control elements to avoid any interference with the flow control elements. The prior art lacks any disclosure of attempts to reduce the length and weight of a turbine engine by incorporating structural frame elements into the more recent fluidic control or plasma control configurations that do not require as much space claim as the conventional variable-pitch configurations. Accordingly, it would be desirable to provide improved systems and apparatuses for use in turbine systems that integrate structural frame elements into a variable-vectoring flow control configuration in order to reduce the weight and length of such turbine systems, and in particular the compression section of such turbine systems. Furthermore, other desirable features and characteristics of the systems and apparatuses will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the preceding background.